New Tricks for Old Bones

Physical activity is good for bones. This is especially true in children, teens and young adults, whose bones are still developing or are at their peak. In older people exercise may at least help slow or prevent further bone loss. And exercise can improve muscle strength, balance, and postural stability, all of which help reduce the risk of falls and thus fractures in those who have had age-related bone loss.

The standard bone-healthy advice is to do “weight-bearing” exercise. That means anything you do against the force of gravity—usually exercise done while on your feet. Lack of gravity explains why astronauts, in the weightless environment of a space capsule for long periods, lose bone mass even if they exercise regularly there. Conversely, obese people tend to have less bone loss because their bones have to bear more weight.

Activities involving muscle force also stimulate bone building. That includes strength training and “impulse” exercise (as in hitting a tennis ball). Of course, these two ways of applying stress to bones (via gravity or muscle force) are not mutually exclusive. When bones are put under stress, this triggers specialized cells to build bone. The benefit is site-specific, so that when you run, the bone growth occurs primarily in your legs; when you play tennis, more occurs in your dominant arm.

How much your bones benefit depends on many factors—including heredity, sex, diet, and age (bones respond most to exercise in younger years). It also depends on the type of exercise you do.

Note: If you have osteoporosis, arthritis, or other physical problems, discuss your exercise options with your doctor and/or a physical therapist before attempting high-impact workouts.

How activities stack up

The more load on the bones, the greater the effect. Thus, high-impact or resistance (also called high-load-bearing) workouts are best for bones.

Here’s a ranking, based in part on guidelines from the Surgeon General:

The distinctions are not always clear-cut, however. For instance, rowing, swimming, and yoga, when done strenuously, can be more beneficial than indicated here. Keep in mind, too, that low-impact activities may still help slow bone loss and have other positive effects on bone health. And activities such as tai chi can help prevent fractures because they improve balance, neuromuscular coordination, and postural stability, thus reducing the risk of falls.

Getting a jump on bone health

Most osteoporosis prevention studies have focused on hip fractures, which involve the upper portion of the thigh bone (femur). The best activities to strengthen the thigh bone are those involving jumping or hopping, research has found. The simplest options are jumping rope or even just short bouts of hopping in place from one foot to the other.

For instance, in a 2010 English study in the journal Bone, when premenopausal women took 50 hops on one foot on most days of the week for six months, bone mineral density in that leg increased markedly, compared to the leg they didn’t hop on. Especially good is multi-directional jumping—as in sports where you change direction a lot, such as tennis, soccer, and some kinds of dancing—because it stresses bones from different angles.

Split up your workouts?

Some research, mostly in animals, has found that short bouts (10 to 15 minutes) of vigorous weight-bearing exercise, with at least three hours between them, are more effective than one long session. Bone has cellular “mechanosensors” that react to physical strain by directing new bone formation.

But the sensors apparently become desensitized to a given load after a short while. Resting between shorter workouts gives these cells time to become desensitized to stimuli. This suggests that it’s better to do short sprints instead of a long jog. And if you don’t have time to get to a gym, short bone-friendly workouts a couple times a day may be just as effective.

Get at least 30 minutes of physical activity on most days, preferably daily.

Incorporate 50 three-inch jumps into your daily workouts. If you can’t tolerate high-impact activities, run or do stair climbing instead.

Include weight-training exercises that use all major muscle groups; increase the resistance gradually over time.

If you enjoy them, do recreational activities such as tennis, hiking, or basketball.

In addition, add extra weight-bearing exercise into everyday activities—by parking farther away in the parking lot, for example, or taking the stairs instead of the elevator.

Bottom line: If bone strength is a key concern for you, try to do short bouts of high-impact activities most days of the week. For instance, hop or jump for five to ten minutes; jumping rope is a good option. Still, if you’re older, frail, and/or have joint pain or a poor sense of balance, such high-impact activities may be out of the question. In that case, your main fitness goal should be to build muscle strength and improve balance to reduce the risk of falls. At a minimum, you should do weight-bearing exercise (walking for the spine and legs, for example, and weight training for the upper body) at least three times a week. Even small gains in bone strength may be enough to reduce your risk of fracture.